Leading American bike trade site Bicycle Retailer have reported that Shimano have succesfully patented a sealed frame design that allows the frame to store pressurized air for operating their pneumatic “Airlines” shift system.
Currently “Airlines” uses a frame mounted canister to drive the rear mech. This avoids cable drag and mud problems but has a limited number of shifts before it’s pressure drops, making it suitable for downhill use only.
The new patent uses a charging valve near the top of the seat cluster and an outlet valve on the chainstay by the rear mech giving a much greater volume of compressed air to work with.
How they’ll get round the problem of sealing the frame or how widespread they intend use of the system to become is unknown, but if anyone can pull off compressed air shifting on a global scale it’s probably Shimano.